Carrier fluid is a major constitutent in the liquid toner used in electrophotography. This carrier fluid evaporates during usage, from both the machine and from the print on paper, thereby causing contamination of the surrounding atmosphere. Furthermore, liquid toned prints, when placed on a table top or other surface, can cause oil slicks to appear on the surface due to initial evaporation and subsequent condensation. Additionally the liquid vehicle tends to spread to give a halo appearance, especially on colored paper. There has been a longfelt need to solve these problems, but that has not been done prior to the present invention without a severe decrease in the quality of print.
This air pollution problem was recognized at least as early as 1973, when U.S. Pat. No. 3,741,643 described a pneumatic assembly for removing excess developer liquid from photoconductor surfaces.
As shown in U.S. Pat. No. 5,308,729, and other patents referred to therein, a known carrier fluid for liquid toner is mineral oil. It has not been possible, however, to find a mineral oil that has both a low enough volatility to avoid pollution and a low enough viscosity to be useful as a carrier fluid.